Volatile Substance Filter
A volatile substance filter comprises volatile substance adsorber material particles on plastics material support surfaces extending parallel to the direction of gas flow through the filter.
This invention concerns volatile substance filters.
Volatile substances occur in the air (gas) of enclosed spaces and if present in sufficient concentrations can represent a danger to health of people and animals breathing the air.
In general industry, chemical plant and in exhaust systems of engines, unwanted volatile substances are also required to be removed from a gas. This may be to prevent their emission into the atmosphere for safety or to prevent them from taking part in chemical reactions at a later stage in a process. It is often, therefore, desirable to reduce the concentration of volatile substances in gases.
Various solid materials (adsorbers) are currently used to adsorb undesirable volatile substances. Among these materials is activated carbon, which is prepared in such a way as to contain a large number of internal voids whose surface area can trap volatile substances.
The adsorber solid materials represent a dense mass, which is relatively impenetrable to gas. The gas pressure drop caused by the density of the intrinsic adsorber material is too high for practical applications, as fans, blowers or other gas movers capable of blowing gases through the adsorber material would be too costly, consume impractically high levels of power and cause unacceptable levels of noise in forcing the gas at a practical velocity through the adsorber material.
Current methods of deploying adsorbers, therefore, attempt to reduce the pressure drop that occurs when gas is forced through the adsorber material. All these methods attempt to reduce the pressure drop by arranging the adsorber material so that it is distributed in space in such a way as to allow the passage of gas through or past the adsorber material particles without requiring the gas to pass directly through the solid adsorber material itself. This results in a practical volatile substance filter. It will be noted that in all these methods the gas passes substantially in a direction orthogonal to the largest surface of a support structure for the adsorber material and the arrangement of passages through this structure is essentially random and tortuous.
There are a number of methods of deploying adsorber material in current use, including reticulated or open-cell foams, adsorber granule beds, adsorber granule biscuits, perforated adsorber granule biscuits and carbon cloths.
Reticulated foam is a plastics material that is formed with an open cell structure. Adsorber material particles are applied in the form of a fine powder and adhered to the inner surfaces of the foam cells. Gas can be forced through the structure, and volatile substances are thus adsorbed into the adsorber particles.
Adsorber granule beds are formed by sandwiching adsorber granules between two retaining grids or meshes that allow the passage of gas blown by, for example, a fan. The mesh size of the grid is chosen so that the adsorber granules are mechanically retained between the grids, while the gas is allowed to pass through the perforations in the surface of the grid and, therefore, through the adsorber granules. The gas comes into close proximity with the adsorber granules and volatile substances are adsorbed into the adsorber granules. However, the gas flow path is tortuous and the same pressure drop problem occurs as described above.
Adsorber granule beds are designed with dimensions orthogonal to the direction of gas flow larger than the depth of the bed in the direction of gas flow. These ratios are kept large in order to minimise pressure drop.
Adsorber granule biscuits are formed from adsorber granules only. The mass of granules may be adhered together by means of heat treatment and/or pressure and/or adhesive applied during manufacture. The biscuit is formed into a shape suitable for the intended application with dimensions orthogonal to the direction of gas flow larger than the depth of the biscuit in the direction of gas flow. These ratios are kept small in order to minimise pressure drop.
Perforated adsorber granule biscuits are formed in the same way as the adsorber granule biscuits described above but with the modification that voids are formed in the biscuit that do not contain adsorber granules. Typically these voids can be of 4 mm diameter and spaced at 8 mm centres and pass entirely through the biscuit in the direction of gas flow. Typically the depth of the biscuit in the direction of gas flow is around 2-12 mm. The voids allow gas to pass relatively more freely than through the adhering mass of granules, with the result that the greater proportion of the gas flow actually passes through these voids. This significantly reduces the efficiency with which the adsorber material adsorbs the volatile substances compared to forcing the gas between the adhering adsorber granules without voids. Again the biscuits are designed with dimensions orthogonal to the direction of gas flow larger than the depth of the biscuit in the direction of gas flow. These ratios are kept large in order to minimise pressure drop further.
Carbon cloth is prepared from cotton or other cloth, which is carbonised by means of a combination of chemical and heat treatment. Typically the weave of the cloth leaves voids in the array of stitching, which allow gas to pass through the cloth. The carbonisation results in imparting to the cloth the properties of an adsorber material. Volatile substances are adsorbed as the gas passes through the cloth. The cloth is woven with dimensions orthogonal to the direction of gas flow larger than the depth of the cloth in the direction of gas flow. These ratios are kept large in order to minimise pressure drop further.
The efficiency of volatile substance adsorption obtained with any of the above-described methods can be very low, typically less than the order of 10%. It can be seen, therefore, that it is difficult to produce a volatile substance adsorbing filter with low pressure drop and high adsorption efficiency.
An object of the present invention is to provide a volatile substance filter that may have improved adsorption efficiency, reduced pressure drop and longer lifetime compared to the above-described prior art filters.
According to the invention it is proposed that a volatile substance filter have volatile substance adsorber material on support surfaces extending in a direction of gas flow through the filter.
Filters according to this invention are particularly appropriate for use in the air cleaning and HVAC (Heating, Ventilation and Air Conditioning) industries where available space for a filter may be limited and where it would be advantageous to have minimal resistance to the air flow.
In preferred embodiments of this invention adsorber material particles are adhered to surfaces extending in the gas flow direction, especially parallel to the direction of gas flow. The support surfaces are, therefore, preferably oriented with respect to the gas flow direction, so as always to present a geometrically minimum possible area of the support surface in resistance to the flow of gas. This is in contradistinction to the prior art filters, wherein the gas flow is substantially orthogonal to their supporting structures and the gas velocity vectors in the proximity of adsorber material support surfaces are oriented in random directions relative to the surfaces. This difference allows pressure drops obtained in the present invention to be significantly lower than prior art filters.
The adsorber material support surfaces may be formed from a suitable plastics material for economy and lightness of weight. The support surfaces may be of thin cross section typically from 0.05 to 0.3 mm, preferably about 0.1 mm thick. This thin cross section leads to a low resistance to gas flow presented by the support surfaces keeping overall pressure drops low.
In one preferred embodiment the support surfaces are in tubular form. Such tubular support surfaces may be of cylindrical, triangular, square, hexagonal or other polygonal cross section.
In other preferred embodiments the support surfaces may be provided by an array of substantially parallel support surfaces arranged so that gas can flow across each surface. Such an arrangement may allow the support surfaces to be brought close together without an undesirable increase in pressure drop. This is because the gas can pass between the surfaces in a direct, straight, smooth and often laminar flow. This is in contradistinction to the tortuous paths and potentially turbulent flows of prior art filters, which result in unwanted pressure drops.
In filters of the invention gas containing volatile substances may, therefore, flow along and substantially parallel to the support surface and volatile substances in the gas flow immediately adjacent to the adsorber particles adhered to the support surfaces may be adsorbed. This results in a reduction in the concentration of volatile substances in the gas stream adjacent to the support surfaces and a concentration gradient orthogonal to the direction of gas flow results with a minimum concentration of volatile substances at the surface rising at greater distances from the surface. The natural result is a rapid diffusion of volatile substances along the concentration gradient towards the support surfaces. Thus, the concentration of volatile substances in a direction parallel to the support surface will also decrease rapidly with distance, as the gas flows along the surface, and high adsorption efficiencies result. Such an array of support surfaces also provides in total a large surface area on which adsorber material particles can be adhered. From these considerations it can be seen that the present invention provides a volatile substance filter, which may operate at high efficiency and low pressure drop while purifying at a practical rate useful volumes of gas.
It will be noted that in volatile substance filters according to the present invention, the gas containing volatile substances may pass substantially in a direction parallel to the largest surface of the structure, which supports the adsorber material, and the arrangement of the passages through this structure may be essentially direct and straight.
The support surfaces may be separated by separator walls, preferably plastic, also of small thickness presenting a low resistance to the gas flow.
An array of support surfaces may be formed by a simple process of extrusion in the form of a fluted plastics sheet. In another specific embodiment alternate flutes are omitted and short stubs of flute material left at each side as spacers.
Adsorber particles used in filters of the invention are preferably in a range of sizes from millimetres to 0.1 micron. It may be advantageous to use a specific size of particle or size range for different purposes. In one preferred embodiment 0.1-0.2 mm activated carbon particles are used. The particles may be adhered to the support surfaces by a method of partially melting the support surface, by using adhesive or by means of electrostatic attraction. The support structure may be filled with adsorber particles and softened in, for example, a heated oven or a microwave oven, then cooled. This attaches the particles without the need for an adhesive. If an adhesive is used it is preferably of low volatile substance emission type, such as, for example, a latex, acrylic or water based contact adhesive, silicone based adhesive or wax.
In an array of support surfaces, the surfaces are preferably separated by a distance of from 0.1 mm to 20 mm, especially from 2 to 4 mm and more especially of about 2 mm. Where the support surfaces are separated by separator walls, they are preferably spaced apart by a distance of from 0.5 mm to 20 mm, especially from 2 to 6 mm and more especially about 2 mm.
The volatile substance adsorber material used in the invention may be any suitable material, of which activated carbon particles or granules is a preferred example. Other materials, such as zeolites, silica gel, calcium chloride, or any similar hygroscopic or deliquescent material or special materials for removal of specific gases may also be used as the adsorber material in the present invention.
Preferred filters according to the invention will also include means for urging gas flow therethrough, such as a fan.
This invention will now be further described, by way of example only, with reference to the accompanying drawings, in which:
Referring to
Turning to
Alternatively, as shown in
It will be noted that the basic elements (shown in
Alternatively, as shown in
It will be noted that the basic elements (shown in
A filter was made according to the embodiment of a circular cross-section tube (as in
In
One specific filter embodiment (
Other embodiments have used glues instead of this heat-fusing process, using a latex, acrylic or water based contact adhesive, silicone based adhesive or wax.
Filters according to the invention should be simple to manufacture, be of low cost and have structural stability. Prior art filters can provide high efficiencies but with the penalties of too high a pressure drop or too deep a filter. To make an improvement in efficiency, pressure drop and filter lifetime an understanding is needed of the variables that may affect them. The variables acting on the filter are as follows:
For Efficiency:
-
- Filter Aperture size (76 on
FIG. 9 , typically 2 mm) - Filter depth (72 on
FIG. 9 , typically 20-75 mm) - Filter aperture wall thickness (typically 0.1-0.5 mm)
- Air Velocity, usually referred to as the ‘Face Velocity’ the velocity of air going through the filter as measured on the leading or trailing face (typically 2 m/s)
- Adsorber particle size (typically 0.1-0.2 mm)
- Adsorber particle type (typically activated carbon)
- Adsorber particle mass in filter (typically 10 g for a 52×67×20 mm filter)
- Adsorber particle adhesion method (typically by fusing to plastic, PVA glue)
- Volatile challenge substance used (typically 2,2,4 trimethylpentane)
- Concentration of volatile challenge used during testing (typically 50 ppm)
- Duration tested (typically no more than 2 mins at these concentrations)
- Filter Aperture size (76 on
-
- Filter Aperture size (typically 2 mm)
- Filter depth (typically 20-75 nmm)
- Filter aperture wall thickness (typically 0.1-0.5 mm)
- Air Velocity, usually referred to as the ‘Face Velocity’ the velocity of air going through the filter as measured on the leading or trailing face (typically 2 m/s)
- Adsorber particle size (typically 0.1-0.2 mm)
- Adsorber particle mass in filter (typically 10 g for a 52×67×20 mm filter)
-
- Adsorber particle size (typically 0.1-0.2 mm)
- Adsorber particle mass in filter (typically 10 g for a 52×67×20 nm filter) volatile substance loading
- Volatile substance filters of the invention may have a variety of applications and may be included in domestic air cleaners and air conditioning systems.
Claims
1. A volatile substance filter comprising volatile substance adsorber material on support surfaces extending in a direction of gas flow through the filter.
2. A filter as claimed in claim 1, wherein the support surfaces are parallel to the direction of gas flow.
3. A filter as claimed in claim, wherein the adsorber material support surfaces are formed from plastics material.
4. A filter as claimed in claim 3, wherein the support surfaces are of thin cross section.
5. A filter as claimed in claim 4, wherein the support surfaces are 0.05 to 0.3 mm thick.
6. A filter as claimed in claim 4, wherein the support surfaces are 0.1 mm thick.
7. A filter as claimed in any one of claims 1 to 6, wherein the support surfaces are in tubular form.
8. A filter as claimed in claim 7, wherein the tubular support surfaces are of cylindrical, square or other polygonal cross section.
9. A filter as claimed in any one of claims 1 to 6, wherein the support surfaces are provided by an array of substantially parallel support surfaces arranged so that gas can flow across each surface.
10. A filter as claimed in claim 9, wherein the support surfaces are separated by separator walls.
11. A filter as claimed in claim 10, wherein the separator walls are of plastics material.
12. A filter as claimed in claim 10 or 11, wherein the separator walls are of small thickness.
13. A filter as claimed in claim 10, 11 or 12 comprising an array of extruded fluted plastics sheet material.
14. A filter as claimed in claim 13, wherein alternate flutes are omitted and stubs of flute material left at sides as spacers.
15. A filter as claimed in any one of claims 1 to 14, wherein the adsorber material particles are in a range of sizes from millimetres to 0.1 micron.
16. A filter as claimed in any one of claims 1 to 15, wherein the adsorber material is activated carbon particles of 0.1 to 0.2 mm size.
17. A filter as claimed in any one of claims 1 to 16, wherein the adsorber material particles are adhered to the support surfaces by partially melting the support surfaces.
18. A filter as claimed in claim 17, wherein the support surfaces are partially melted in a heated oven or a microwave oven.
19. A filter as claimed in any one of claims 1 to 16, wherein the adsorber material particles are adhered to the support surfaces by electrostatic attraction.
20. A filter as claimed in any one of claims 1 to 16, wherein the adsorber material particles are adhered to the support surfaces by adhesive.
21. A filter as claimed in claim 20, wherein the adhesive is of low volatile substance emissions type.
22. A filter as claimed in claim 21, wherein the adhesive is selected from latex, acrylic or water based contact adhesives, silicone based adhesives and wax.
23. A filter as claimed in claim 19, wherein the adsorber material particles are charged electrically prior to adhesion.
24. A filter as claimed in claim 23, wherein the support surfaces are oppositely charged electrically to facilitate adhesion.
25. A filter as claimed in any one of claims 9 to 24, wherein the support surfaces are separated by a distance of from 0.1 mm to 20 mm.
26. A filter as claimed in claim 25, wherein the support surfaces are separated by a distance of from 2 to 4 mm.
27. A filter as claimed in claim 25, wherein the support surfaces are separated by a distance of about 2 mm.
28. A filter as claimed in any one of claims 10 to 27, wherein, when the support surfaces are separated by separator walls, the separator walls are spaced apart by a distance of from 0.5 mm to 20 mm.
29. A filter as claimed in claim 28, wherein the separator walls are spaced apart by a distance of from 2 to 6 mm.
30. A filter as claimed in claim 28, wherein the separator walls are spaced apart by a distance of about 2 mm.
31. A filter as claimed in any one of claims 1 to 30, wherein the volatile substance adsorber material is activated carbon particles or granules.
32. A filter as claimed in any one of claims 1 to 30, wherein the adsorber material is a hygroscopic or deliquescent material.
33. A filter as claimed in any one of claims 1 to 30, wherein the adsorber material is selected from zeolites, silica gel and calcium chloride.
34. A filter as claimed in any one of claims 1 to 33 including means for urging gas flow therethrough
35. A filter as claimed in claim 34, wherein the urging means is a fan.
36. A volatile substance filter substantially as hereinbefore described with reference to and as illustrated in any one of FIGS. 5 to 10 of the accompanying drawings.
Type: Application
Filed: Jul 13, 2006
Publication Date: Feb 5, 2009
Applicant: VALERION 2 LIMITED (Lancashire)
Inventors: Geoffrey Norman Walter Gay (Fairfield, IA), George Griffiths (Lancs)
Application Number: 11/995,776
International Classification: B01D 53/04 (20060101);